1. Field of the Invention
The present invention relates to an apparatus and a method for mass spectrometry analysis, in which a substance immobilized on a surface of a base plate is exposed to laser light and is desorbed from the surface, and the desorbed substance is captured to be analyzed. The present invention further relates to a base plate for mass spectrometry analysis, which is used in such apparatuses and methods.
2. Description of the Related Art
As a conventional method for detecting the presence and the like of a specific substance in a sample, Raman spectroscopy is known, and a description of the Raman spectroscopy is found, for example, in U.S. Patent Application Publication No. 20060001872. The method described in this document uses a dielectric base plate that has metal particles distributed on a surface thereof. The sample is contacted with the surface of the base plate, and then the surface is exposed to laser light to generate Raman scattered light. The thus generated Raman scattered light is subjected to spectroscopic detection. Based on the detected spectrum, whether the specific substance is adhering on the base plate surface is determined, and further, the molecular structure or the like of the substance is analyzed. Using the dielectric base plate having metal particles distributed on the surface thereof in this method, local plasmon is excited at a portion of the metal particles exposed to the laser light, and the Raman scattered light is significantly enhanced by the local plasmon resonance to allow highly accurate analysis.
It should be noted that, besides using the dielectric base plate having metal particles distributed on the surface thereof, as described above, the similar Raman scattered light enhancing effect utilizing the local plasmon resonance can be obtained by using a base plate including a metal surface having a micro-pattern including numerous convex and concave portions fabricated thereon, or a base plate describes in U.S. Patent Application Publication No. 20050105085, which has numerous micropores formed in the surface of a dielectric body thereof and metal particles filled in the micropores such that head portions of the metal particles, each having a size larger than a diameter of the micropores, project from the dielectric surface.
On the other hand, as a conventional apparatus for performing mass spectrometry analysis of a substance, a Time of Flight Mass Spectrometer (TOF-MAS), as described, for example, in Japanese Unexamined Patent Publication No. 9(1997)-320515 is known. The TOF-MAS carries out mass spectrometry analysis of a substance based on a time of flight that is acquired by exposing the substance immobilized on the surface of the base plate to laser light or the like to desorb the substance from the surface, and detecting a time taken by the ion of the desorbed substance to fly a predetermined distance.
It is likely that, after the presence of a specific substance in a certain sample is detected by using the above-described Raman spectroscopy, the mass of the substance is analyzed by using, for example, the above-described TOF-MAS. In such a case, it is naturally necessary to perform mass spectrometry analysis without mistaking the substance whose presence has been detected for another substance. It should be noted that International Patent Publication No. WO97/009608 has proposed a mass spectrometry analysis method in which the same base plate is used for substance detection according to Raman spectroscopy utilizing surface plasmon resonance and for mass spectrometry analysis using a TOF-MAS.
According to the mass spectrometry analysis method disclosed in International Patent Publication No. WO97/009608, a specific substance, whose presence in a sample has been confirmed using Raman spectroscopy, can reliably be subjected to mass spectrometry analysis without mistaking the substance for another substance. However, this method has a drawback in that high-power laser light is necessary to ionize the substance immobilized on the surface of the base plate to desorb the substance from the surface.